# A stone fell from a helicopter at a height of 30m. how long will it take for the stone to reach the ground

March 25, 2021 | education

| **A stone fell from a helicopter at a height of 30m. how long will it take for the stone to reach the ground if the helicopter was descending at a speed of 5 m / s.**

Data: h (altitude at which the helicopter was) = 30 m; V0 (helicopter descent speed) = 5 m / s.

Constants: g (acceleration due to gravity) ≈ 10 m / s2.

The duration of a stone falling after being dropped from a helicopter can be calculated by the formula: S = h = V0 * t + a * t ^ 2/2 = V0 * t + g * t2 / 2.

Substitute the known values: 30 = 5t + 10 * t ^ 2/2.

5t ^ 2 + 5t – 30 = 0 | : five.

t ^ 2 + t – 6 = 0.

By Vieta’s theorem: t1 = 2 s (true); t2 = -3 s (wrong).

Answer: The dropped stone will reach the ground in 2 seconds.

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